Powder Metallurgy - Post 2

Characteristics of Metal Powder
1.Particle Shape : shapes may be special nodular , irregular , angular & dendritic. It influence the flow characteristics of powder
. 2.Particle Size : Influence the control of porosity , compressibility & amount of shrinkage . It is determined by passing the powder through the sieves or microscopic measurement .

3.Particle Size Distribution : Specified in term of sieve analysis , the amount of powder passing through 100, 200 etc mess sieves.
4. Flow rate : ability of powder to flow readily & conform to the mould cavity .
5. Compressibility : Defined as volume of initial powder to the volume of compact part.
6.Apparent Density : Depends on the particle size & is defined as the ratio of volume to weight of loosely filled mixture.
7. Purity : Impurities reduce the life of dies & affect the sintering process. Oxides & gaseous impurities can be removed from part during sintering .
BASIC Powder Metallurgy Steps

PRODUCTION OF POWDERS
• Metal powders => Main constituent of a P/M product; final properties of the finished P/M part depends on size, shape, and surface area of powder particles
• Single powder production method is not sufficient for all applications
Powder production methods
: 1. Mechanical methods, 2. Physical methods, 3. Chemical Methods 1. Mechanical methods
=> cheapest of the powder production methods; These methods involve using mechanical forces such as compressive forces, shear or impact to facilitate particle size reduction of bulk materials; Eg.:Milling Milling
: During milling, impact, attrition, shear and compression forces are acted upon particles. During impact, striking of one powder particle against another occurs. Attrition refers to the production of wear debris due to the rubbing action between two particles. Shear refers to cutting of particles resulting in fracture. The particles are broken into fine particles by squeezing action in compression force type. Main objective of milling
: Particle size reduction (main purpose), shape change, agglomeration (joining of particles together), solid state alloying, mechanical or solid state mixing, modification of material properties.